In this article you will learn everything that is currently known about the lithosphere (the rigid layer that makes up the tectonic plates of the world), its characteristics, parts, function and importance.
What is the lithosphere?
The lithosphere or lithosphere is the outermost layer of the planet earth in the dynamic model of the layers of the earth, it is characterized because it includes the earth’s crust and a part of the upper mantle (lithospheric mantle) that behaves like a rigid solid.
Se compone de dos capas o partes: la litosfera continental y la litosfera oceánica.
This layer is “floating” on the asthenosphere, which is a layer with plastic behavior, while the lithosphere has a rigid mechanical behavior.
The lithosphere, is the layer that dynamically belongs to the processes of plate tectonics, that is to say that this layer is responsible for the fact that the continents move on the asthenosphere in the dynamics of plate tectonics.
Therefore, the partition of the lithosphere forms what is known as lithospheric plates, which is the same as tectonic plates.
The terrestrial lithosphere It is characterized by being a solid, rigid and relatively cold layer, which has a density of approximately 5 gr/cm3 and has an average thickness of around 100 km, being thicker on the continents, reaching up to 150 km.
Characteristics and properties
Types, layers or parts of the lithosphere
The lithosphere is divided into 2 main parts, the continental lithosphere and the oceanic lithosphere.
Just as the crust is divided into oceanic and continental, the lithosphere is equally divided in the same way.
Thus, the continental lithosphere comprises the continental crust and a part of the upper mantle, while the oceanic lithosphere comprises the oceanic crust and a part of the upper mantle.
structure of the lithosphere
As seen in the image, the lithosphere is above the asthenosphere, and includes the crust (oceanic and continental) and a part of the upper mantle.
That part of the upper mantle that makes up the lithosphere is characterized by being equally rigid and for this reason it is added to the crust to form the lithospheric plate.
While the asthenosphere is the upper part of the mantle but has a plastic behavior.
The plastic behavior of the asthenosphere allows the lithosphere to move and generate the movement of tectonic plates.
Boundaries
The limits of the lithosphere can be defined thanks to the speed and behavior of the seismic waves “P”.
It can be observed that the P waves progressively increase their speed in the lithosphere, due to the fact that this layer behaves rigidly.
While in the asthenosphere an extreme reduction in the speed of the “P” waves is observed in an area known as the “zone of low wave speed”.
This zone marks the lower limit of the lithosphere and the beginning of the asthenosphere.
The lower limit of the lithosphere is between 100 km and 150 km deep, that is to say that in that area the P waves slow down.
Depth and thickness
The depth and thickness of the lithosphere are around 100 to 150 km, the 100 km are related to the oceanic lithosphere, while the 150 km are usually found in the continental lithosphere.
Lithological composition
If we take into account that the base of the lithosphere comprises the upper part of the mantle, then it is clear that this part would be made up of ultramafic rocks, such as peridotites.
Now, if we talk about the oceanic lithosphere, it is clear that this layer would be made up of rocks similar to the ophiolitic sequence such as son, gabbros and basalts.
While, if the continental lithosphere is analyzed, it is clear that this layer would be made up of rocks typical of the continents such as granite, diorite, tonalites, and mainly metamorphic rocks.
Density
The difference in density between the oceanic and continental lithosphere is important because this allows the oceanic lithosphere to slide under the continental lithosphere in a process known as subduction.
Therefore, it can be concluded that the oceanic lithosphere is denser than the continental lithosphere.
Temperature and pressure
The temperature in this layer is constantly increasing and usually reaches around 1200°C. In fact, it is in the upper part of the mantle that partial fusion processes begin to be created.
While the pressure is possibly up to 0.5 million atmospheres, which is low if we compare it with that of the core that reaches 3.6 million atmospheres.
Continental lithosphere
The continental lithosphere It is a layer made up of the continental earth’s crust and a part of the upper mantle.
It is characterized by having a thickness that reaches 150 km, especially in the center of the continents where the continental cratons are located, which are the oldest areas of the continents.
Lithologically it is made up of a mixture of intrusive igneous rocks of acid to intermediate composition (batholiths) and metamorphic rocks.
In plate tectonics the continental lithosphere It is the one that is always on the oceanic lithospheric plate, and is responsible for the continents moving in global dynamics.
Oceanic lithosphere
The oceanic lithosphere It is a layer made up of the oceanic terrestrial crust and a part of the upper mantle.
Its thickness is much less compared to the continental lithospheric plate and is around 100km.
However, the density is greater than that of the continental lithospheric plate and it is because of this that this layer tends to sink below the continental lithosphere in a process known as subduction.
This process is responsible for creating earthquakes, volcanoes, and for the recycling of rocks in the crust.
Lithologically it consists mainly of gabbros and peridotites.
Function and importance
The lithosphere and tectonic plates
The lithosphere is important because it is a fundamental part of the theory of plate tectonics which indicates that the continents “lithospheric plates” are in constant motion on the planet.
Currently it is known that the earth’s surface is divided into several tectonic plates, these tectonic plates are actually the lithosphere divided or split into several parts.
The lithosphere and subduction
It is the lithospheric plates that form the subduction processes at the convergent edges of tectonic plates, for this it is necessary that one lithospheric plate be denser than the other.
What usually happens is that the oceanic lithospheric plate subducts or slides under the continental lithospheric plate.
In addition, if it is taken into account that the lithospheric plates move, they are directly related to the occurrence and formation of the different structures and geoforms of the planet earth.